1. Field of the Invention
This invention relates to a disposable syringe, more particularly to a pre-filled disposable syringe for facilitating injection and needle retraction operations with one hand.
2. Description of the Related Art
In U.S. Pat. No. 6,221,055 B1 for a retractable dental syringe, there is disclosed a pre-filled syringe, which includes a barrel, a carpule and plunger assembly that is filled with medication and that is inserted into the barrel from a rear opened end of the barrel and that is communicated with a needle by the carpule is punctured by a rear tip end of the needle, and a push ring for holding the needle in the barrel. At the end of an injection, the plunger is further pressed to move the carpule forwardly so that the push ring is removed to permit retraction of the needle. However, the carpule cannot be accommodated in the barrel in advance, and the carpule and the barrel have to be packed separately for subsequent assembly in use, thereby resulting in increased operation time. In addition, such a syringe structure makes the manufacture of the syringe complicated.
Therefore, in U.S. patent application Ser. No. 11/601,526, the applicants disclosed a disposable syringe with a built-in carpule, which includes a carpule that can be pre-assembled in a barrel so that clinical injection operation by health care workers is simplified and is convenient to conduct. Moreover, after injection, the syringe can be conveniently rendered unreusable after injection, and injection and needle retraction can be conducted smoothly in a single operation.
It is desirable to improve the aforesaid syringe to ensure air- and water-tightness of a medicament chamber so as to eliminate risk of degradation of a medicament contained therein, and to simplify the construction of the syringe.